Here's a bunch of the more prominent shallow water starfish you're inclined to encounter in this region...

Pentaceraster cumingi (aka Oreaster occidentalis). Oreasteridae. Photo by bswift. From Bahía de los Ángeles, Sea of Cortez. This one is interesting-have not seen the yellow highlights. It almost looks like one of the Indo-Pacific species...
Image by cam17 from the Galapagos.
and this "frosted" variant. Image by cam17 from the Galapagos

This next pic is something special! You can probably not see this anywhere but in the Panama area (where there are both Atlantic and Pacific coasts)!!

The yellowish-orangish individual on the left? is the tropical ATLANTIC Oreaster reticulatus. Vs. the deep red individual on the right which is the tropical PACIFIC Pentaceraster cumingi (also called Oreaster occidentalis in the past). They are closely related.. and possibly sister-species separated by the Panamanian land bridge/isthmus!

There are VERY few places in the world where you would you be able to see them BOTH alive in the same place at the same time. I would be curious to know where this was shot...

Nidorellia armata aka the "chocolate chip star". Oreasteridae. Photo by cam 17. From the Galapagos
Another great image by billamp. Pic from off San Carlos Mexico.Close up on Nidorellia. This terrific image by Scott Trageser (NatureStills) shows tiny ophiuroids (possibly Ophiactis?) living on the spines! Not sure, but these might be something new?

At one time, there was one species of crown-of-thorns starfish which occurred from Baja California to Southern Japan/Hawaii all the way to the east coast of Africa! Nowadays, genetics tells us there are likely multiple cryptic species that morphology may or may not be able to distinguish..

But people always seem a little surprised when they see something like a starfish in motion! Most times, starfish move slowly if at all and so if people see one being the lamborginhi of echinoderms, it generally provokes some curiosity...

Why should we care?? Doesn't this all seem like kind of an...odd thing to know? Indeed. But rate of movement is actually an important bit of information in understanding feeding biology, ecology, and food webs. How fast do the predators go compared to their prey? How far could an adult travel on its own and disperse its gametes in a discrete amount of time? So, yeah. Its worthwhile...

It should be noted that most of the rates outlined below are based on a clip motivated by predators. So, its not necessarily clear what their "average cruising speed" would be..

Most of the observed species (which are intertidal-shallow species like Patiria miniata or Leptasterias) seem to run on the slow to moderate side, about 0.3 to 1.3/2.0 mm/s and are medium-sized but relatively few of the smallest or largest species were included.

Diversity isn't well sampled and we really only know the movement rates of VERY few species (17 out of 1900 species!).

Its thought that larger size does have some relationship to speed and some of the fastest species listed are also among the largest..

Here's a breakdown of speeds in starfish in milimeters per second!

Honorable Mentions:
I should just say that while these seem reasonable-it seems like there are faster species out there. These just seem to be well-known and as more information becomes available there's likely to be starfishes that put these guys to shame...Astropectenaranaceus and others.Speed: 2.5 (error+/-0.8)Astropecten is the "proper" sand star. They occur on unconsolidated sand/sediments where they sit and wait, buried until prey comes along. They occur in shallow-water, tropical to temperate water habitats all over the world.

There are many species..many of which are deceptively fast...Here is a nice video of A. aranaceus which is found primarily in European waters..

But here is Astropecten polyacanthus from the tropical Indo-Pacific. Look at that thing go!

Asterias forbesi and Asterias rubens (Asteriidae). Speed: 2.0 mm/s and 3.3 mm/s
These two species are the most commonly encountered in the North Atlantic-so on the east coast of the United States and in Europe. These are the classically known "starfish prey on a bivalve" type of starfish that you see in the intertidal.

Here's video from Massachusetts showing Asterias moving around at a decent but relatively slow clip..

Oreaster reticulatus (Oreasteridae). Speed: 3.3 mm/s
This species is the well-known "cushion star" found in the tropical Atlantic-Gulf of Mexico, Bahamas, etc. Its primarily an opportunistic omnivore feeding on algae and other organics present on the bottoms.

This was honestly kind of a surprise. On the spectrum of starfish that are known for speed-this one isn't one of them. But the original account observed them in undisturbed, natural settings, so perhaps there is some bias on my part...

TOP FIVE FASTEST KNOWN Starfish!
Of the known movement rates listed in Montgomery and Palmer's paper these were the 5 highest with embellishment from what I've seen etc. Bear in mind this is 5 of the best known species, out of nearly 1900 different species-so..there's possibly (probably) faster or at least, comparably fast taxa out there....5. Protoreaster nodosus (Oreasteridae). Speed: 4.6 mm/s (deviation +/- 1.2)
This is the well-known "Chocolate Chip Starfish" that occurs in the tropical Indo-Pacific. This species is often encountered in the aquarium and tropical tourist trade. It is related to the "Cushion star" O. reticulatus above..and similarly, feeds on microalgae and lives on loose, sandy bottoms.

The video doesn't show them at their quickest but its something..

4. Acanthaster planci (Acanthasteridae).Speed: 8.3 mm/s (deviation +/-2.5)
This is the infamous Crown of Thorns Starfish which occurs throughout the tropical Indo-Pacific from Hawaii and Baja California all the way to the east coast of Africa in the Indian Ocean. Its a large, fast, coral eating predator..

Archaster is parallel/convergent with Astropecten (below) but live in a similar habitat buried or semi-buried in loose sediment/gravel...There's a nice account of biology here by my friends at Wild Singapore..

2. Pycnopodia helianthoides (Asteriidae). Speed: 20.4 mm/sPycnopodia is found only on the west coast of the United States from Alaska to southern California. Its a big animal-up to about 2-3 feet in diameter.

Its a big animal and boasts 15,000 tube feet on its 20-30 arms. Its a feared and voracious predator on mollusks, sea urchins and other invertebrates, which can actually smell it coming and will move out of the way when they do...

It has THE reputation for being the fastest starfish known.. but as we shall see, this is not the case...

here's some footage of this formidable species in motion!

1. Luidia ciliaris and friends (Luidiidae). Speed: 50 mm/s !!Luidia is a genus of "sand star" that lives in tropical to temperate, usually shallow sandy habitats all over the world. They are predators that feed on mollusks, sea urchins and other invertebrates.

L. ciliaris occurs in the North Atlantic around Europe-the UK and so thereabouts..

So, not what you thought! Pycnopodia has gotten the reputation as the "fastest starfish" in the world.
But NOT so! It would seem that Luidia spp. overall seem to be among the fastest of sea stars with a rate of movement just short of twice as fast as Pycnopodia!

First the 6 armed Meyenaster gelatinosus (an asteriid related to Pisaster or Asterias)

Picture by azulprofundo5170

and the heliasteridHeliaster helianthus

Photo by Maurice André

So, let's get right to it!
Basically the sea urchin T. niger was observed in surprisingly high abundance living on elevated rock surfaces.

So, tops of boulders, rocks and so on..especially relative to the two aforementioned well-known sea star predators H. helianthus and M. gelatinosus. Their Figure 1 shows the proportion of overall "high surfaces" were covered by sea urchins relative to their predators..

The reason for this unusual difference in the location of sea urchins vs. sea stars. Why do so many sea urchins live on elevated rockfaces??? This cartoon from Echinoblog Art Dept. explains it best!

Predatory starfish approaches up the cliff face! Sea urchins can SMELL predators approaching based on the odor of the predator brought up via water currents. They SENSE that something bad is coming...

The urchins are trying to prevent THIS from happening!!!!

Meyenaster feeding on Tetrapygus. Image by Azulprofundo5170

Here we have some T. niger amidst some yummy kelp on a vertical (presumably elevated) rockface...

Tetrapygus niger photo by Jabaezam

When it becomes clear that the starfish is out for some good sea urchin eatin or when it just starts to ATTACK! (i.e. the predator is in direct or close contact) the urchins DETATCH from the rock face and let the gravity do the rest!!!

In other words they JUMP For it!! Drop and ROLL!
(note that the Echinoblog Art Dept. reconstruction below is somewhat exaggerated..)

This immediately removes the threat of the oncoming predator and puts a pretty solid distance between the predator and the prey!

The starfish is of course, unable to just "release" its tube feet since they are more flattened in shape and holding on with their bottom surface!

Kind of clever, eh?

Here is the graph (their Figure 3A) that shows an experiment that showed how many sea urchin detatchments occurred when they artificially motivated the sea urchins to detatch in reaction to predators and parallel control actions.

Thus, the "jump" response happened only in reaction to direct contact with predators and not simply the "smell" of them approaching

Figure 3B (above) shows what happened after contact but without detachment. Their behavioral cue was to proceed higher up the boulder.

Its worth noting that Just because the urchins would "fall" did not guarantee their overall survival or even escape. Spines or other structures could break. And if an urchin falls upside down and a starfish happens to be there? Yikes!

Interestingly, the "detatch" and "get carried away by the current" approach is also seen in starfish vs. starfish interactions, snail vs. starfish interactions and in other sea urchins.

Some Dynamics!

Various experimental trials showed some further depth..

Of the two sea star predators-Meyenaster gelatinosus was regarded as the greater threat to the sea urchins. Heliaster (the sun star) illicited an escape response (i.e., the sea urchin moves away VERY quickly once it senses the predator) but not as severe as the one that Meyenaster did.

Meyenaster's preference is to be on lower ground (it moved there when placed on boulders) whereas the urchins preferred to live on elevated surfaces such as boulders and so forth..

Sea urchin survival was considered higher on elevated surfaces and is considered to be primarily a defensive behavior since food is actually rare on these elevated surfaces (contrary to the picture above).

It turns out that fish are ALSO predators of these sea urchins which at one time may have preyed upon the urchins on top of the rocks, boulders and elevated surfaces..

One interesting observation by the authors was that owing to the overfishing of various fish predators, there may be an increase in the overall abundance of sea urchins. This in turn may have led to the "importance" of these starfish as predators in the observed ecosystem.

People often wonder why little natural history stories like this are important? This gives us some perspective on the importance of how removing fish can conceivably cascade into something more.

There were MANY different invertebrate taxa that were shown to interact with those sea urchins. Understanding even a small segment of the interaction might be important to understanding how changes in the ecology have shifted their community structure..

Tuesday, July 10, 2012

So..Washington DC has been having a string of annoyingly potent thunder/lightning storms over the last week. I had some good stuff in prep but I've only just gotten power back.

So, rather than try and half-ass a post I thought it would be better to treat you to some incredible photos of feather stars aka crinoids. These are filter feeding echinoderms that use their long arms to pick food out of the water.

Crinoids have been around for a long while with fossils dating back to the Paleozoic. You may recognize fossil crinoids by their long stalk.. but most recent crinoids are unstalked and are basically a cup with a bunch of arms emerging from the top surface...

The one drawback to showing crinoids for me, is that a specimen is usually needed for identification-so many of these will have to go nameless for now..

About Me

I pursue starfish related adventure around the world with a critical eye and an appreciation for weirdness.
Support has been courtesy of the National Science Foundation but the views and opinions presented herein are mine and do not reflect the opinions of them or any affiliated institutions.
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